I know turbine engines (bearings) are cooled by oil jets and that when oil is scavenged from the bearings it is more of a mist than a liquid, hence the need for various types of de-aerating this mist to produce oil once again. So is there a need for fuel de-aerating? Especially in fighter jets, because they maneuver a lot, will this cause the fuel to churn in its wing, causing the fuel pump to suck in a lot of air?

As an add on, I read from multiple sources tanks in wings can operate in high-g situations simply by having multiple fuel ports leading out of them. I find this a little confusing. Let's say a fighter is dashing, so all the fuel in its tank is rushing to the rearmost part of the tank. If this tank has a front and a back fuel port, and they are being sucked by the same pump, will this result in something like a 50/50 fuel/air mixture? This has to be dealt with, or the combustor will hiccup, or even worse the flame will back travel into the fuel line and bust it open, am I right?

PS: I know all about baffling, so please don't include this in your answer, thanks!


1 Answer 1


There are ways of preventing air from being pulled into fuel lines due to change in speed, direction, or orientation. On of the simplest is called a "clunk" line, which is a flexible hose with a weighted fuel inlet at the end. The inlet and fuel simply fall to the "lowest" level G forces take it.

As far as fuel entraining air by agitation, important factors are viscosity and the chemical make up of the fuel. Fuel is generally "thinner" than oil so air can escape more easily. Chemically, fuel does not have the tendency to form bubbles as a mixture of soap and water would. Air entrainment simply is not an issue with flight maneuvers. No doubt the oil companies have a good number of chemists to keep it that way.

  • $\begingroup$ well then it has more to do with physical attributes of the fuel than any fuel system design, however contrived the latter might be. I wonder if you design a liquid-fueled SAM that can do 40g how do you keep it fueled at all time? If you have ever seen real footage of free air combat war game, you couldn't even find the horizon for most of the time because the fighter maneuver so much everything is blurry solely from motion blur, the g-force is never stable, but constantly randomly pointing at any and all directions. $\endgroup$ Jan 17, 2019 at 6:51
  • $\begingroup$ I guess that is why "fighter manuever" G forces are tough for pilots. Solid fuel also helps too. $\endgroup$ Jan 17, 2019 at 11:58
  • $\begingroup$ @MeatballPrincess SAMs rarely pull those manoeuvres while the engine is burning, and while it is, the thrust is mostly aligned with the axis of the missile. In a terminal guidance scenario, which is when the lateral loads will spike, the rocket engine will most likely have burned out anyway. Additionally, many (most? I'd have to check) use solid fuel as it is easier to keep on combat readiness. $\endgroup$ Jan 17, 2019 at 15:15

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